1. Field of the Invention
The present invention relates to the light-sensing field, and specifically, to a multi-depth-of-field light-sensing device, a light-sensing system using the multi-depth-of-field light-sensing device, a depth of field extension method, and an optical imaging system and method.
2. Related Art
The present invention is continuation to “multi-spectrum light-sensing device and manufacturing method for same” (PCT/CN2007/071262), “multi-spectrum light-sensing device and manufacturing method for same” (Chinese Application No: 200810217270.2), “multi-spectrum light-sensing device” (Chinese Application No: 200910105372.X), “multi-spectrum light-sensing device and sampling method for same” (Chinese Application No: 200910105948.2), and “light-sensing device and reading method for same, and reading circuit” (Chinese Application No: 200910106477.7) applied by the inventor at an earlier time, aiming to provide implementation of a more specific and preferable multi-spectrum light-sensing device at a chip and system grade.
A light-sensing system is a system which captures and collects a scene through an optical lens, and records the scene through a light-sensing device, such as a CMOS light-sensing chip. When the light-sensing system is working, a procedure of adjusting the lens to enable a scene at a distance from the lens to be clearly imaged is called focusing, and a point where the scene is located is referred to as a focusing point. “Clearness” is relative, so an image of a scene at a certain distance in front of (closer to the lens) or behind the focusing point can be clear, and the total sum of these front and rear ranges is referred to as depth of field. Generally the front depth of field is less than the rear depth of field, namely, after precise focusing, a scene only in a very short distance in front of the focusing point can be clearly imaged, while a scene in a very long distance behind the focusing point is clear.
A system for obtaining a clear image at a wide depth of field is one of research objectives of people for a long time. Research indicates that, the magnitude of the depth of field is relevant to the focal distance of the lens, a lens with a long focal distance has a small depth of field, and a lens with a short focal distance has a large depth of field. It can be seen that, to adjust the focal distance of the lens is one of means for obtaining a clear image at a wide depth of field; additionally, according to a basic imaging formula of geometrical optics
            1      f        =                  1        u            +              1        v              ,(where f is the focal distance of the lens, u is the object distance, namely, a distance from a shot object to the lens, and v is the image distance, namely, a distance from the lens to the light-sensing device), it can be seen that, to dynamically adjust the image distance is also one of means for obtaining a clear image at a wide depth of field.
Therefore, the automatic focusing manner in the existing light-sensing system adopts one of the foregoing two means. For example, a lens is formed of a group of lens elements, and the distance between the lens elements is adjusted, so that the focal distance of the lens or the image distance (between the lens and the light-sensing device) can be adjusted (to implement optical zooming or focusing); or a CMOS light-sensing device for example is driven to shift, thereby changing the image distance (to implement optical focusing). However, evidently, focusing of these two manners both needs an electrically operated mechanism and a complex and precise mechanical component to drive shift of the lens elements or the light-sensing device. In this way, not only is the size prominently increased, but also cost and power consumption are prominently increased. In many applications, such as a mobile phone camera and a medical camera, these increases are obvious unfavorable factors.
Some wide depth of field systems without adopting any motion mechanism are therefore proposed in an attempt to replace the automatic focusing demand in some applications. This system is called EDoF (Extended Depth of Focus) in the application of a mobile phone camera. For example, in an EDoF system proposed by the DXO corporation, through particular lens design, red light-sensing pixels in a light-sensing device are focused at an infinitely far place, and blue light-sensing pixels are focused at a near distance as much as possible (such as 50 cm). However, green light-sensing pixels are focused at an intermediate location. In this way, no matter where an object is located, there is always an image whose color is distinct or relatively distinct. Afterwards, through a mathematical means, a distinct color is taken as a main body, and an insufficiently distinct color is taken as auxiliary information, so that a distinct image can be restored and calculated in a wide range.
However, if a single-layered light-sensing device is adopted, when red light-sensing pixels are focused at an infinitely far place, it is generally very difficult to make the focusing distance of blue light-sensing pixels less than 50 cm. Furthermore, for a light-sensing device adopting a Bayesian pattern, red pixels and blue pixels only each account for ¼ of light-sensing pixels. Therefore, when it is required to take red or blue as the main body of definition calculation, the resolution of an image is already reduced to a value below a half of the resolution obtained when green is taken as the main body. It can be seen that, this solution has some limitations.
Therefore, it is still necessary to improve the existing light-sensing device or system.